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Chapter 3 Lecture
Earth Science
Fourteenth Edition
Rocks: Materials
of the Solid Earth
Jennifer Mangan
James Madison University
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Rock Cycle
• Shows the interrelationships among the three rock
types
• Earth as a system: the rock cycle
– Magma
• Crystallization
– Igneous rock
• Weathering, transportation, and deposition
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Rock Cycle
• Earth as a system: the rock cycle
– Sediment
• Lithification
– Sedimentary rock
• Metamorphism
– Metamorphic rock
• Melting
– Magma
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Rock Cycle
• Earth as a system: the rock cycle
– Full cycle does not always take place due to “shortcuts” or
interruptions
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e.g., Sedimentary rock melts
e.g., Igneous rock is metamorphosed
e.g., Sedimentary rock is weathered
e.g., Metamorphic rock weathers
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The Rock Cycle
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Igneous Rocks
• Form as magma cools and crystallizes
– Rocks formed inside Earth are called plutonic or intrusive
rocks
– Rocks formed on the surface
• Formed from lava (a material similar to magma, but without
gas
• Called volcanic or extrusive rocks
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Igneous Rocks
• Crystallization of magma
– Ions are arranged into orderly patterns
– Crystal size is determined by the rate of cooling
• Slow rate forms large crystals
• Fast rate forms microscopic crystals
• Very fast rate forms glass
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Igneous Rocks
• Classification is based on the rock’s texture and
mineral constituents
– Texture
• Size and arrangement of crystals
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Igneous Rocks
• Types of igneous textures
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Fine-grained – fast rate of cooling
Coarse-grained – slow rate of cooling
Porphyritic (two crystal sizes) – two rates of cooling
Glassy – very fast rate of cooling
Vesicular – contains hole left by gas bubbles
Pyroclastic – fragmented; produced by consolidation of
volcanic fragments
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Fine-Grained Igneous Texture
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Coarse-Grained Igneous Texture
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Porphyritic Igneous Texture
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Glassy Igneous Texture
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Vesicular Igneous Texture
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Pyroclastic Igneous Texture
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Igneous Rocks
• Classification is based on the rock’s texture and
mineral constituents
– Mineral composition
• Explained by Bowen’s reaction series which shows the order
of mineral crystallization
• Influenced by crystal settling in the magma
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Bowen’s Reaction Series
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Classification of Igneous Rocks
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Igneous Rocks
• Naming igneous rocks
– Granitic rocks
• Composed almost entirely of light-colored silicates – quartz
and feldspar
• Also referred to as felsic: feldspar and silica (quartz)
• High silica content (about 70 percent)
• Common rock is granite
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Granite and Granitic Rock
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Igneous Rocks
• Naming igneous rocks
– Basaltic rocks
• Contain substantial dark silicate minerals and calcium-rich
plagioclase feldspar
• Also referred to as mafic: magnesium and ferrum (iron)
• Common rock is basalt
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Basaltic Lava
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Igneous Rocks
• Naming igneous rocks
– Other compositional groups
• Andesitic (or intermediate)
• Ultramafic
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Sedimentary Rocks
• Form from sediment (weathered products)
• About 75 percent of all rock outcrops on the continents
• Used to reconstruct much of Earth’s history
– Clues to past environments
– Provide information about sediment transport
– Rocks often contain fossils
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Sedimentary Rocks
• Economic importance
– Coal
– Petroleum and natural gas
– Sources of iron and aluminum
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Sedimentary Rocks
• Classifying sedimentary rocks
– Two groups based on the source of the material
• Detrital
• Chemical
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Sedimentary Rocks
• Detrital rocks
– Material is solid particles
– Classified by particle size
– Common rocks include
• Shale (most abundant)
• Sandstone
• Conglomerate
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Detrital Sedimentary Rocks
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Sedimentary Rocks
• Chemical sedimentary rocks
– Derived from material that was once in solution and
precipitates to form sediment
• Directly precipitated as the result of physical processes, or
• Through life processes (biochemical origin)
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Sedimentary Rocks
• Common chemical sedimentary rocks
– Limestone – the most abundant chemical rock
– Microcrystalline quartz (precipitated quartz) known as
chert, flint, jasper, or agate
– Evaporites such as rock salt or gypsum
– Coal – compressed plant material
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Chemical, Biochemical, and Organic
Sedimentary Rocks
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Sedimentary Rocks
• Sedimentary rocks are produced through lithification
– Loose sediments are transformed into solid rock
– Lithification processes
• Compaction
• Cementation by
– Calcite
– Silica
– Iron Oxide
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Sedimentary Rocks
• Features of sedimentary rocks
– Strata, or beds (most characteristic)
– Bedding planes separate strata
– Fossils
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Traces or remains of prehistoric life
Are the most important inclusions
Help determine past environments
Used as time indicators
Used for matching rocks from different places
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Metamorphic Rocks
• “Changed form” rocks
• Produced from preexisting
– Igneous rocks
– Sedimentary rocks
– Other metamorphic rocks
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Metamorphic Rocks
• Metamorphism
– Takes place where preexisting rock is subjected to
temperatures and pressures unlike those in which it
formed
– Degrees of metamorphism
• Exhibited by rock texture and mineralogy
• Low-grade (e.g., shale becomes slate)
• High-grade (obliteration of original features)
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Metamorphic Grade
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Metamorphic Rocks
• Metamorphic settings
– Contact, or thermal, metamorphism
• Occurs near a body of magma
• Changes are driven by a rise in temperature
– Regional metamorphism
• Directed pressures and high temperatures during mountain
building
• Produces the greatest volume of metamorphic rock
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Metamorphic Rocks
• Metamorphic agents
– Heat
– Pressure (stress)
• Confining pressure – from burial
• Differential stress – occurs during mountain building
– Chemically active fluids
• Mainly water and other volatiles
• Promote recrystallization by enhancing ion migration
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Confining Pressure and Differential Stress
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Metamorphic Rocks
• Metamorphic textures
– Foliated texture
• Minerals are in a parallel alignment
• Minerals are perpendicular to the compressional force
– Nonfoliated texture
• Contain equidimensional crystals
• Resembles a coarse-grained igneous rock
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Development of Foliation due to Directed
Pressure
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Metamorphic Rocks
• Common metamorphic rocks
– Foliated rocks
• Slate
– Fine-grained
– Splits easily
• Schist
– Strongly foliated
– “Platy”
– Types based on composition (e.g., mica schist)
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Common Metamorphic Rocks
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Metamorphic Rocks
• Common metamorphic rocks
– Foliated rocks
• Gneiss
– Strong segregation of silicate minerals
– “Banded” texture
– Nonfoliated rocks
• Marble
– Parent rock is limestone
– Large, interlocking calcite crystals
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Metamorphic Rocks
• Common metamorphic rocks
– Nonfoliated rocks
• Marble
– Used as a building stone
– Variety of colors
• Quartzite
– Parent rock – quartz sandstone
– Quartz grains are fused
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Resources from Rocks and Minerals
• Metallic mineral resources
– Gold, silver, copper, mercury, lead, etc.
– Concentrations of desirable materials are produced by
• Igneous processes
• Metamorphic processes
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Resources from Rocks and Minerals
• Metallic mineral resources
– Most important ore deposits are generated from
hydrothermal (hot-water) solutions
• Hot
• Contain metal-rich fluids
• Associated with cooling magma bodies
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Resources from Rocks and Minerals
• Pegmatites
– Result from crystallization in fluid-rich environment
– Unusually large crystals
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Resources from Rocks and Minerals
• Types of deposits include
– Vein deposits in fractures or bedding planes, and
– Disseminated deposits which are distributed throughout
the rock
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Metallic Resources
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Resources from Rocks and Minerals
• Nonmetallic mineral resources
– Make use of the material’s
• Nonmetallic elements
• Physical or chemical properties
– Two broad groups
• Building materials (e.g., limestone, gypsum)
• Industrial minerals (e.g., fluorite, corundum, sylvite)
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Energy Resources: Fossil Fuels
• Coal
– Burns energy stored by plants millions of years ago
– Air pollution
– Surface scarring
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Energy Resources: Fossil Fuels
• Oil and Natural Gas
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More than 60% of U.S.-consumed energy
Remains of marine plants and animals
Source rock – where oil and natural gas originate
Oil trap – geologic environment allowing oil and gas to
accumulate
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Energy Resources: Fossil Fuels
• Oil trap – two basic features
– Reservoir rock
• Porous and permeable
• Yields oil and gas in significant quantities
– Cap rock
• Impermeable
• Keeps oil and gas from surface escape
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Energy Resources: Fossil Fuels
• Common oil and natural gas traps
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Anticline – up-arched sedimentary strata
Fault trap – displaced strata
Salt dome – includes layers of rock salt
Stratigraphic (pinchout) trap – original sedimentation
pattern
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Common Oil Traps
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Energy Resources: Fossil Fuels
• Hydraulic Fracturing
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“Fracking”
Shatters shale with significant gas and petroleum reserves
Pumping liquids into rock at very high pressure
Can include toxic chemicals
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